1. Field of the Invention
The present invention relates to a method for reclaiming an investment casting wax composition, and in particular to a method for recovering and reclaiming a wax component and a filler from a used investment casting wax composition containing the filler, which is liberated during a dewaxing process using an autoclave. The invention also relates to a reclaimed investment casting wax composition.
2. Description of the Related Art
Investment casting is a known technique for performing precision industrial casting. In this process, precise products are produced by forming a wax pattern having the same shape as the final product, by use of a silicone rubber matrix or a die, and covering the wax pattern with a refractory ceramic material. The wax covered with the refractory ceramic material pattern is then heated to remove the wax (dewaxing), and a mold made from the refractory is produced. Finally, a metal melt is cast into the mold to produce a precise product.
Dewaxing is generally performed by placing the ceramic-coated mold into an autoclave and heating with steam to a temperature of 150.degree. C. to 180.degree. C. to melt and remove the wax. The steam dewaxing process permits recovery and reclamation of wax. The reclaimed wax is reused to produce another pattern.
The recovered wax contains a variety of impurities, e.g. mold sand, iron scale generated during the autoclave treatment, and water introduced during the steam treatment. The recovered wax, therefore, must be purified before it can be reused for further molds. In recent years, an investment casting wax composition containing a polystyrene filler with an average particle size of 40 .mu.m has been used in an amount of 20 to 30% by weight, to improve thermal conductivity of the wax and to prevent formation of sink marks at the heavy-gage section of the pattern. Since such a composition is expensive, reclamation of the used investment casting wax composition is now more important.
Industrial reclaiming processes for used investment casting wax compositions include sedimentation processes, centrifugal processes, and filtration processes. In sedimentation processes, a used investment casting wax composition is melted by heat so that impurities sink, and the supernatant (upper) layer is recovered. A sedimentation process requires that the used investment casting wax composition be maintained at a high temperature of higher than 100.degree. C. for a day or more. This time-consuming process has some further disadvantages, such as degradation of the wax component and an inability to recover filler. On the other hand, the centrifugal process and the filtration process also cannot recover fillers, and have a further disadvantage of low recovery yield of wax, although they allow the processing time to be shortened.
Japanese Patent Laid-Open No. 56-139253 discloses a method for recovering wax used in an investment casting process, in which wax removed from an autoclave is rapidly cooled to be frozen, and then water in the wax is sublimated in a vacuum atmosphere to remove water from the wax. Japanese Patent Laid-Open No. 7-39992 discloses a method for purifying used wax, in which used wax removed from an autoclave and water are injected into a mixer, are mixed while feeding air to pulverize the used wax, and the pulverized wax is melted to separate the impurities.
These conventional processes do not contemplate recovery of the filler from a filler-containing wax that has been recently used. Thus, the conventional processes do not permit reuse of the filler and wax adhered to the filler. Supply of fresh filler is therefore necessary for reuse of the reclaimed wax composition according to the above processes. As described above, generally 20 to 30% of expensive organic filler is compounded in a wax composition, from which only the wax is recovered, and at a low yield. Thus, the conventional processes do not satisfy the demand of cost reduction by wax reclamation. Furthermore, the dumping of the residue including fillers causes an increased environmental impact.